In the above disk apparatus, a voice coil motor (thereafter abbreviated as VCM) of an actuator used to drive a head receives nearly constant or very low frequency bias forces during the track following operation by the head. These bias forces are caused by a circulating air stream which passes through an arm assembly whereby the head is connected to VCM, and the motion of a flexible cable for conveying input or output signals from the head to electronic circuits. Also, there is an offset voltage with respect to a power amplifier which provides a control current to VCM. The above bias and offset voltage cause a steady error in the disk apparatus.
Japanese Published Unexamined Patent Application (PUPA) No. 62-257682, and the corresponding U.S. Pat. No. 4,679,103 disclose that a stiffness integrator wherein a head position error signal is integrated, is inserted in a feedback loop when a head is positioned within the range close to half of a track width from the center line of a target track.
PUPA No. 63-23280 and the corresponding U.S. Pat. No. 4,697,127 disclose that if the current sector and the previous sector are denoted by k+1 and k, respectively and a head position for sector k(equivalent to a position error (PES)) is X1(k), an integrator which outputs an integrated position X4(k+1) with respect to sector (k+1), shown by the following equation: EQU X4(k+1)=X4(k)+X1(k)
(That is, X4 is a total of sequentially added X1.)
is provided and the integrated position signal which is an output from the integrator is combined with a head position (error) signal and an estimated speed signal in track following mode to generate a signal that indicates the magnitude of a current to be inputted to the VCM of the actuator whereby the head is driven.
As disclosed in PUPA No. 62-257682, PUPA No. 63-23280, an integrator is provided in the feedback loop in the track following mode in order to cancel the above steady error. However, insertion of the integrator in the loop causes an overshoot. Thus, if head position control is performed using a integrating signal for a position error signal when the speed of the head is too high, an excessive overshoot will occur and thereby a settling time for the head will increase.
An object of this invention is to provide method and apparatus for controlling a position of a head in order to prevent an excessive overshoot from occurring when the speed of the head is too high during a follow track operation.